I have a Athlon 64X2 3800 at 2.01GHz CPU, the EVGA 9800GTX card, 4Gb of Muskin Ram, and a monitor at 1440X900 resolution. Lately i have been downloading and trying out demos from steam and the disc from the PC Gamer Magazine. However, I discovered that my PC can't really run game demos, such as Bioshock, Empire: Total War, and Codename Panzer -Cold War, really smooth at high settings. As a result, i am wondering that is it that my ancient duo core CPU is bottlenecking my 9800GTX card. Moreover, at high settings, i actually get 60FPS in Bioshock, but the framerate often drops to 10FPS once every 5s to 10sec. Thus, the Bioshock demo kindof runs laggy for me. My computer can also only get 10FPS to 15FPS in Codename Panzers demo. Nevertheless, i can run Tom Clacy's Hawx demo at 40FPS smoothly without problems. Fallout 3 and Dawn of War II (full game) also runs pretty good on high settings for me. Generally, i am wondering that is it that my CPU is too slow and bottleneck my 9800GTX card. Or is it that i run the games at 1440X900 that cause the unsmoothless and sudden drop of FPS in games.

Would i solve the bottleneck problem if i upgrade it to Anthlon X2 6400+ at 3.2GHz? or a Phenom with quad or triple core cwould be better?

~i was acutally about to by the 6400+ duocore when i went to the states ~

The 6400+ wouldn't be worth it. I went from a 3800+ @ 2.7GHz to a E6420 @ 3.2GHz and the X2 was absolutely slaughtered. I'm on i7 now, but that's a different story altogether. Anyways, most high-end single GPU cards see a bottleneck right around the C2D 3.2GHz mark, and considering the C2D's slap the X2's around, I wouldn't consider the 6400+ much of an upgrade from what you have, especially if you're willing to go for a Phenom II triple or quad.

__________________For my part I know nothing with any certainty, but the sight of the stars makes me dream.

The 6400+ wouldn't be worth it. I went from a 3800+ @ 2.7GHz to a E6420 @ 3.2GHz and the X2 was absolutely slaughtered. I'm on i7 now, but that's a different story altogether. Anyways, most high-end single GPU cards see a bottleneck right around the C2D 3.2GHz mark, and considering the C2D's slap the X2's around, I wouldn't consider the 6400+ much of an upgrade from what you have, especially if you're willing to go for a Phenom II triple or quad.

my motherboard is M2N-E from Asus, don't think it can support Phenomon II... I think it can only support Phenomon if i change the Bios. Would the Phenom eliminates the bottleneck though?